Effect of condensed tannins from Birdsfoot trefoil and dietary protein level on growth performance, carcass composition and meat quality of ram lambs

Abstract The study aimed to evaluate the interaction between dietary crude protein (CP) and condensed tannins (CT) on the growth performance, carcass composition and meat quality of ram lambs. Twenty-four White Alpine lambs were fed a basal diet consisting of 56% birdsfoot trefoil (BT) silage and 44% hay (67.1% grasses, 4.3% legumes and 28.6% herbs). In addition, lambs were offered either a barley concentrate to reach the predicted protein requirements (BP) or a barley and soybean meal concentrate to extend the CP level 20% above the requirements (HP). The diets were either untreated (BP − ; HP − ) or treated (BP + ; HP + ) with the CT-binding polyethylene glycol (PEG). Lambs fed HP − and HP + diets had greater ( P − and BP + diets. Consequently, slaughter weight and cold carcass weight were greater ( P  ≤  0.05) in HP − and HP + groups. Despite similar slaughter weight, lambs fed BP − and HP − diets had lower ( P + and HP + diets. The skatole concentrations in the perirenal fat were not affected by the dietary treatments. The observed interaction between CP level and CT concentration resulted in lower ( P − diet, attributed to the greater CT intake. No effects of dietary treatments were detected on the flavour scores of the meat whereas the loin from lambs fed HP − and HP + diets had lower ‘sheepy’ odour compared with the loin of those fed the BP − and BP + diets. These findings let us conclude that at elevated intake, CT reduced the indole but not skatole level in the perirenal fat. The lack of effect of BT at basal and high dietary CP level on the other traits investigated might be explained by the rather low CT content.